1. Field of the Invention
The invention relates generally to a multilayer dentifrice composition containing reactive ingredients and more particularly to a striped toothpaste of improved storage stability containing reactive peroxide and bicarbonate ingredients.
2. The Prior Art
Aesthetic effects have been acknowledged to play an important role in consumer acceptance of many products. In many cases ornamental effects have been used to distinguish particular products in the market place and identify products having particular distinct properties. In the dentifrice field, toothpastes and gels having contrasting stripes are known. Such stripes provide an aesthetic effect which the user finds pleasing and promotes the use of the dentifrice, particularly by children. Although such products have met with consumer approval, it has been found difficult to formulate striped dentifrice products when the ingredients in the toothpaste composition are reactive as in the case of dentifrice compositions containing peroxide compounds. For example, it has been found to be very desirable to incorporate peroxide compounds in dentifrice compositions, the efficacy of peroxide compounds in oral hygiene having long been recognized. Such compounds have been proven effective in the treatment of gingivitis, periodontitis and in combating plaque. Additionally, peroxide compounds have been utilized for oral cosmetic purposes such as tooth whitening which results from bleaching and cleansing of tooth surfaces. A problem encountered with dentifrices formulated with peroxide compounds, is that the peroxides tend to bleach the dyes incorporated in the dentifrice for striping effect causing undesirable fading and discoloration of the stripe.
In addition to the color fading problem, when peroxide compounds are utilized in combination with conventionally employed constituent ingredients of dentifrices such as alkaline abrasive agents such as sodium bicarbonate, the tendency of the peroxide compounds to react with such other ingredients presents significant problems and difficulties are encountered with respect to providing products which achieve adequate shelf life.
Examples of prior art attempts at providing stable peroxide containing dentifrices in which a bicarbonate ingredient is also included are found in the disclosures of U.S. Pat. No. 4,971,782, U.S. Pat. No. 4,897,258 and U.S. Pat. No. 4,837,008.
U.S. Pat. No. 4,837,008 discloses an aqueous dentifrice containing a peroxide and/or bicarbonate ingredient in which the ingredients are provided with a barrier coating to prevent reaction of the ingredients. A disadvantage to such dentifrice is that release of the ingredients for cleaning effect during use is diminished by the presence of the barrier coating.
U.S. Pat. No. 4,897,258 discloses an anhydrous dentifrice containing calcium peroxide and sodium bicarbonate wherein the anhydrous state of the dentifrice prevents reaction between the ingredients. A disadvantage to such dentifrice is that in spite of the anhydrous state of the dentifrice, limited storage stability is experienced.
U.S. Pat. No. 4,971,782 discloses an anhydrous dentifrice containing peroxide and bicarbonate ingredients in which one of the ingredients is coated with a water dissolvable coating and a peroxide stabilizer is included in the dentifrice to further enhance storage stability. In spite of the presence of the stabilizer, the dentifrice remains deficient in storage stability required for commercial use.
Because of the storage stability problems with dentifrices containing reactive ingredients such as peroxides and bicarbonate compounds, dentifrices containing either the peroxide or bicarbonate compound are separately maintained before use. For example, U.S. Pat. No. 4,687,663 discloses placing each of a peroxide gel and bicarbonate paste into separate compartments of a single two-compartment container to avoid interaction between these ingredients before use. Such dual packaging devices are costly to manufacture and attempts at simultaneous even delivery of the two separate dentifrice components from the dual compartmented device is many times erratic.
There is therefore a need in the art for a dentifrice containing peroxide and other reactive ingredients such as bicarbonate salts which dentifrice remains stable during storage for extended periods of time and can be stored without provision for costly physical separation of components.